According to the Bible, Hezekiah, in response to attack by Assyria, cut
off the springs that flowed into the city of Jerusalem1
and built a tunnel to bring water into the city:

As for the other events of Hezekiah's reign, all his achievements and
how he made the pool and the tunnel by which he brought water into the
city, are they not written in the book of the annals of the kings of
Judah? (2 Kings 20:20)

Since
King Hezekiah reigned between 727 B.C. and 698 B.C., the tunnel should
have been built about that time. However, skeptics have long said that the
tunnel was built much later, claiming that an inscription at the end of
the tunnel dated it to second century B.C.2

However, science has come to the rescue with a definitive date.
Geologist Amos Frumkin and colleagues3
collected plants preserved in the waterproof layers of plaster lining the
tunnel and determined the carbon-14 date. In addition, stalactites were
collected and their ages determined through uranium-thorium dating. The
plant was dated at 700-800 B.C., whereas a stalactite was dated to 400
B.C.
(It would have been expected to have formed after the tunnel was built.)

The dating of the Siloam Tunnel is a remarkable testimony of the
accuracy of the biblical texts and positively refutes the skepticism of
archeologists who are constantly challenging biblical narratives. How many
other times will they be proved wrong?

References

When Hezekiah saw that Sennacherib had come and that he intended to
make war on Jerusalem, he consulted with his officials and military
staff about blocking off the water from the springs outside the city,
and they helped him. A large force of men assembled, and they blocked
all the springs and the stream that flowed through the land. "Why
should the kings of Assyria come and find plenty of water?" they
said. (2 Chronicles 32:2-4)